Place eggs, chives, milk in a bowl and whisk with fork, set aside.
Heat a small non-stick pan with cooking spray and sauté onion and mushrooms until softened and set aside.
Spray the pan again and pour in egg mixture, cooking on low heat, approx 4-5 minutes or until the egg has cooked nearly through. Flip over or place under grill to cook other side.
Once cooked to your liking, slide onto a plate; add the mushroom/onion mix and spinach.